Trapezoidal fill sheet for low silhouette cooling tower

ABSTRACT

The vertical height requirement of a cooling tower is reduced by utilizing trapezoidal shaped fill sheets which are suspended generally in line with the entering air stream so as to form a wedge shaped plenum space beneath the lower sloped edges of the fill sheets.

BACKGROUND OF THE INVENTION

This invention relates to cooling towers wherein heat is exchangedbetween water and air, and more particularly involves an improvedcounterflow cooling tower with heat transfer media construction andmethod of operation which enables the vertical dimension of the coolingtower to be reduced and improves airflow through the media.

The design of counterflow cooling towers is a well developed technology.In one style of counterflow cooling tower which is widely applied incommercial installations heat transfer media comprising a plurality offill sheets are mounted vertically and slightly spaced so as to providevertical air channels between adjacent sheets, and ambient air is passedupwardly while heated water is flowed downwardly on the surface of thesheets to effect heat exchange to cool the water. The fill sheets havebeen relatively flat parallelograms, usually rectangles, of relativelyimpervious material with surface embossments to keep adjacent sheetsspaced apart and to distribute a film of water on each surface. Suchsheets have been arrayed in a horizontal bank with the lower edgespositioned horizontally and held generally parallel and even with oneanother at a uniform distance above a water sump or pool in the bottomof the cooling tower so as to provide a rectangular plenum for air toenter beneath the fill sheets, as shown, for example, in U.S. Pat. No.3,132,190 to Engalitcheff Jr. Above the bank of fill sheets a waterdistribution network is located and balanced so as to deliversubstantially uniform rates of water flow to all portions of the fillsheets; and above that an air outlet is located.

Rarely do counterflow heat exchangers depart from such an arrangement,although there has been a design for such a unit wherein a pack ofmultiple fill units is shaped to form a sloping bank of interconnecteduniform symmetrical fill sheets arranged with the sheets perpendicularto the entering air flow, as shown in U.S. Pat. No. 3,983,190 toNorback.

It is to be understood that other types of heat transfer media may beemployed in a cooling tower, such as serpentine or coiled tubing whereinanother fluid is circulated, and combinations of fill sheets and tubing.The present invention is also applicable to such other heat transfermedia which is referred to herein collectively as media.

While it is sometimes possible to provide for a natural air draftthrough such a counterflow cooling tower, it is far more common that airis propelled mechanically. This may be by either forced draft, where oneor more fans drive air from one or more sides of the cooling tower intothe plenum below the fill sheets, or induced draft, where one or morefans are mounted above the fill sheets and water distributor and drawair through the plenum and media. In all such instances the air entersthe plenum horizontally and therein gradually turns upwardly to passbetween the media.

A number of factors such as fan shrouding, the dynamics of air flowthrough the fan, and distance from the air inlet contribute to an unevendistribution of air flowing between the media. In the past this hasusually been compensated by maximizing the vertical dimension and spacewithin the plenum, orienting the lowermost media to be perpendicular tothe initial horizontal direction of air entering the cooling towerand/or sometimes positioning control vanes within the plenum. Even so inprior cooling towers the air entering the plenum has tended to movehorizontally beyond the media adjacent the air entry resulting in anarea of media close to the entry way that is relatively starved forvertically moving air and a consequent reduction in efficiency. This hasbeen particularly true of forced draft towers employing centrifugal fanswhich heretofore tended to thrust air with great force toward a far sideof the plenum.

Moreover, it has been found that the overall height of a cooling toweris limited by practical considerations such as the need to reduce riskof wind damage, vertical structural restraints and restrictions at thelocation of installation (space between floors and maximum height forbuildings) and the visual impact of a cooling tower respecting itssurroundings. Another important factor applies to factory constructedcooling towers which are shipped from a manufacturing plant to aninstallation site along rail lines and roadways with vertical limitsimposed by either the carrier equipment or bridges, and the like, alongthe route.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to devise acounterflow cooling tower with a relatively smaller vertical height.

It is also an object of the present invention to devise a counterflowcooling tower and method of operation with a more efficient distributionof air flow through all areas of the media contained therein.

It is another object of the present invention to provide a counterflowcooling tower with a relatively smaller inlet air plenum andnon-symmetrical heat transfer media whereby the height of the coolingtower may be reduced and air distributed more effectively to all areasof the media.

It is a further object of the present invention to provide a counterflowcooling tower with non-rectangular heat transfer media and air plenumwhich interface along a sloped boundary whereby the height of thecooling tower may be reduced and air distributed more effectively to allarea of the media.

It is still another object of the present invention to facilitate theair movement through a counter flow cooling tower by aligning heattransfer media with the incoming air flow and positioning the loweredges of the media at an angle to the horizontal and direction of theincoming air flow.

An even further object of the present invention is to provide a methodfor moving air into a cooling tower and more effectively redirecting theair through heat transfer media therein.

It is yet another object of the present invention to provide an improvedtrapezoidal shaped fill sheet to permit a reduction in the verticaldimension of a cooling tower.

Briefly the present invention allows for a reduction in the overallheight of a counterflow cooling tower by organizing heat transfer mediain a non symmetrical arrangement therein so that a lower boundary of themedia is inclined downwardly toward the bottom of the tower from an airentry side toward a far side of the cooling tower, so as to form asloped interface with a triangular air plenum from which thehorizontally entering air tends to move substantially upwardly uponreaching the media.

Stated differently, the present invention provides for arranging themedia within a cooling tower to slope downwardly from an air entrywayand thereby obstructing incremental layers of air moving horizontallyinto the plenum below the media and turning the incremental air flowupwardly as each layer reaches media interfacing the plenum.

A preferred form of media is fill sheets of trapezoidal shape suspendedso as to be parallel to the direction of entering air flow.

BRIEF DESCRIPTION OF THE DRAWING

Other objects and advantages of the present invention will becomeapparent upon reading the following detailed description in conjunctionwith the drawings wherein:

FIG. 1 is an illustrative side elevation of an induced draft counterflowcooling tower embodying the present invention and containing trapezoidalfill sheets, with an end removed to show interior parts;

FIG. 2 is an illustrative side elevation, similar to FIG. 1, showing aforced draft counterflow cooling tower embodying the present inventionand containing serpentine tube media;

FIG. 3 is an illustrative side elevation of a preferred embodiment ofthe present invention comprising a forced draft counterflow coolingtower with a centrifugal fan and trapezoidal fill sheets;

FIG. 4 is an illustrative side elevation of an induced draft counterflowcooling tower having symmetrical construction with air entry from theopposite sides; and

FIG. 5 is a view of rectangular fill sheet stock, marked for cutting toproduce two trapezoidal fill sheets of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An induced draft counterflow cooling tower is illustrated in FIG. 1wherein a plurality of heat transfer media generally 10 are suspendedwithin a generally rectangular enclosure comprising vertical walls 12, abottom basin 14 (or sump) and an overhead cowling 16 shaped to form atransition cover extending from the walls 12 to an exhaust fan ring 18which surrounds and supports a multibladed fan 20 driven by an electricmotor 22. Normally the motor 22 is mounted on the exterior of thecooling tower so as to be clear of the highly humid air dischargedtherefrom; however the motor 22 may be located within the tower or abovethe fan discharge. As illustrated the motor 22 is supported on thecowling 16 and is drivingly connected to the fan 20 by an endless belt24, or the like, extending between sheaves on the motor shaft and fanshaft.

As shown by the arrows A in FIG. 1, air is drawn horizontally through anentry way 28 in only one side wall into a plenum space 36 within thecooling tower and moves upwardly between the media 10 and exits throughthe fan ring 18. The bottom of the cooling tower comprises an enclosedbasin or sump 14 to receive a descending flow of water that is sprayedon the media 10 from an overhead distribution network comprising a watermain 38, distribution pipes 40 and spray nozzles 42. Water is dischargedfrom the basin 14 through a discharge conduit 48. A plurality of misteliminator baffles 50 is positioned above the media 10 and may beconveniently supported above the water distribution pipes 40.

A preferred form of media 10 in the present invention is non-rectangularfill sheets 58 having trapezoid shaped faces 60 which sheets aresuspended in the cooling tower so as to have a horizontal upper edge 62and a sloped, non-parallel lower edge 64 which extends from a short sideedge 66 downwardly, to an opposite parallel and longer side edge 68. Aplurality of such fill sheets 58 are suspended within the cooling towerwith the short side edges 66 disposed toward an air entry side so thatthe lower edges 64 decline away from the top of an air entry way 28toward the basin 14 thereby forming a sloped boundary and interfacerespecting the plenum space 36.

Thus it will also be understood that the present invention involves anovel method of operation by orienting the interface between heattransfer media and air plenum to slope downwardly from the top of theair entrance side of a cooling tower and thereby resisting continuedhorizontal movement of increments or layers of air and turning suchincrements of air to move upwardly through the media. Further thepresent method involves increasing the depth of the media as thedistance from the air entrance increases (by maintaining the media topsubstantially at a horizontal level) thereby progressively lengtheningboth the horizontal and vertical air paths and hence increasing the flowresistance for successive increments or layers of air entering thecooling tower. This results in a relatively greater amount of air flowupwardly at the air entrance to the cooling tower as compared to towershaving a horizontal interface between media and plenum and an even depthof media across the tower.

It is to be noted that the fill sheets 58 are oriented to position thefaces 60 parallel to the entering air flow (as designated by the arrows"A"). In the illustrated embodiment there are a plurality ofsubstantially identical parallel fill sheets 58 (only one such sheetbeing visible from the side) each extending the full vertical depth ofthe media. It is to be understood, however, that such media may beconstructed of stacked layers (not shown) wherein the upper layer (orlayers) may comprise rectangular sheet components arranged vertically,and either parallel or crosswise to the lowermost fill sheets, so longas the latter present a sloping interface with the air plenum 36.Preferably the sloping interface is obtained by employingnon-rectangular fill sheets and orienting a diverging edge 64 downwardlyacross the plenum 36, and while trapezoidal sheets 60 as shown arepreferred, it is possible to utilize a triangular fill sheet (notshown).

Preferably the mist eliminator baffles 50 are mounted crosswise to thefill sheets (as shown) so as to function to both deflect and guidedischarge air away from the intake air space and collect air entrainedmoisture droplets. However, baffles 50 may be repositioned if air is tobe deflected in a different direction. The water distribution spraynozzles 42 may be adjusted to supply relatively lesser quantities ofwater adjacent the fill sheet short side edges 66 as compared to thelonger side edges 68 to partially balance the effect of the relativecooling paths of increments of water descending along the fill sheetfaces 60 when appropriate to fill height and density conditions.However, that effect is also at least partially balanced by a relativelylower resistance to air flow, and hence greater rate of air flow, acrossthe shorter cooling paths.

Because the preferred fill sheets have sloped lower edges 64 there is atendency for some of the descending water to temporarily collect in theform of beads which run down the lower edge rather than to drop into theplenum space 36. In excessive amounts and circumstances such beading onadjacent fill sheets could bridge the space between sheets and interferewith air flow distribution. To counteract such a possibility the loweredges 64 of interdigitating fill sheets are alternately offset a smallvertical distance (as shown by a phantom line 70 in FIG. 1.

Further details of fill sheets generally 10 are shown in FIG. 5 whichalso illustrates the method by which such sheets with trapezoidal faces60 are made. Formed rectangular stock 80 of plastic film is available asthe usual type of rectangular fill sheet in a wide range of dimensions.Such stock usually is embossed with a uniform pattern of contours 82,which define pathways and generally increase the surface area acrosswhich water is spread in the cooling tower, and one or more stiffeningridges 84 and margins. Also the stock is embossed to include a pluralityof spacer projections 86 extending in two directions perpendicular tothe plane of the sheet which projections nest when the sheets arestacked but serve to keep adjacent sheets spaced apart when suspended ina cooling tower in an offset interdigatating manner. The rectangularstock 80 is cut at an angle, as shown by the dashed line in FIG. 5,between points on opposite sides equally spaced from the longer edgesthereof. The specific dimensions and the slope angle of the non-paralleledge may be adapted to the size limitations of a cooling tower.

In a forced draft embodiment shown in FIG. 2 structural elementscorresponding to those heretofore described are denominated by the samereference character with a prime notation. It will be see that in thisembodiment an air duct 90 extends outwardly from one cooling tower wall12' and a fan 20' is mounted to force air through the duct 90 into theplenum space 36'. In this embodiment the heat transfer media is shown tocomprise parallel rows of serpentine tubes 72 connected between inletand outlet headers 74 and 76, respectively, and aligned with theincoming air. This type of media permits an additional fluid to becooled as it is flowed through the serpentine tubes. It will be notedthat each successive descending run of the serpentine tube 72 isshortened so as to define a sloping interface with the plenum 36'.

FIG. 3 illustrates a preferred embodiment of the present inventionutilizing trapezoidal fill sheets 58" in a forced draft counterflowcooling tower having a centrifugal fan 94. The fill sheets 58 arealigned with the incoming air propelled by the fan 94 through atransition duct 96. It has been found that the horizontal distributionof air from such a fan 94 is improved if the fan shaft 98 is slightlyelevated and the fan discharge aimed through a gradually flaredtransition duct 96 which expands to approximately the dimensions of theinlet side 28" of plenum 36". Another advantage of aligning the fillsheets 60" with the forceful air streams from a centrifugal fan 94 isthat the lower edges 64" of the sheets have a lessened tendency toflutter and thereby air flow between the sheets is facilitated.

An example of a forced draft (centrifugal fan) counterflow cooling towerhaving exterior width and length dimension of 48×713/4 inches (exclusiveof fan and entry duct) and height of 783/4 inches, containing seventyeight (78) trapezoidal fill sheets suspended lengthwise, can supplyapproximately 55.9 tons of cooling capacity by cooling 167.7 gallons ofwater per minute from 95° F. inlet to 85° F. discharge using 15670 cubicfeet per minute of 78° F. ambient air supplied by a centrifugal fandriven with a five (5) horsepower motor. This is believed to represent aheight reduction of eight (8) inches and a capacity increase of morethan 7% over prior cooling towers containing the same number and totalsurface area of fill sheets. A further operating savings is obtainedwith the present invention in that by reducing the height of the coolingtower there is a reduction in the vertical distance that the warm watermust be lifted to the water distribution pipes and nozzles with aconsequent and significant saving of energy required to drive waterpumps.

FIG. 4 illustrates an induced draft cooling tower provided with two airentry ways 28a and 28b at opposite walls 12" of the cooling tower andtwo banks of fill sheets 10a and 10b above plenum spaces 36a and 36b. Asis readily seen the cooling tower is generally symmetrical about acentral vertical plane and parts corresponding to those described inconnection with FIG. 1 are denominated by the same reference characterwith a double prime notation. It is also possible to construct a forceddraft embodiment of a symmetrical unit similar to the induced draftembodiment of FIG. 3.

Further variations and modifications may be made without departing fromthe spirit and scope of the invention which is defined in the followingclaims:

What is claimed is:
 1. An improved substantially flat fill sheet for acooling tower, said fill sheet comprising:a trapezoidal face portionextending between two nonparallel edges and unequal opposite sidesconnected between said edges; said face portion terminating at saidedges and said sides, said face portion having a surface with contoursdefining pathways for a fluid and said face portion including spacerprojections on its said surface.
 2. A pair of fill sheets according toclaim 1, each of said fill sheets having two nonparallel edges ofunequal length and two unequal opposite sides extending substantiallyperpendicular to the shorter of said nonparallel edges, said faceportions of said pair of sheets being substantially congruent along thelonger of said two nonparallel edges and which form a common line ofseverance substantially angularly bisecting a rectangular sheetoriginally comprising said pair.